What Is an Earth Leakage Fault?

Earth leakage is current escaping its intended path and finding a route to earth instead. A small amount of leakage happens in every electrical installation and is completely normal. A larger amount is what makes your RCD trip.

The confusing part is that “earth leakage” gets used for two different situations. Sometimes it means a genuine fault damaged insulation, a failed appliance, water ingress. Other times it means several small, harmless leaks adding up until an RCD becomes sensitive enough to trip on almost nothing. Both get called earth leakage. Only one of them needs a repair.

This guide explains the difference, what causes each, how an electrician measures it, and what it means if you’ve had it flagged on an EICR.

How Does an RCD Detect Earth Leakage?

An RCD works by comparing two numbers: the current going out on the live wire and the current coming back on the neutral. In a healthy circuit, those two numbers match exactly.

When they don’t match, the difference is going somewhere it shouldn’t — usually to earth. The RCD detects that gap and disconnects the circuit, normally within a fraction of a second. Domestic RCDs are set to trip once the leakage reaches 30 milliamps.

That’s the mechanism. It’s simple, and it’s also why the RCD tripping doesn’t automatically tell you why. It only tells you that current is leaking somewhere on that circuit.

Normal Leakage, Excessive Leakage, or a Genuine Fault?

Not every trip means something is broken. There are three different situations, and they call for three different responses.

Normal leakage happens in every installation. Cable insulation, appliance filters and electronic devices all allow a tiny amount of current to leak to earth as part of how they’re built. This is expected and accounted for in the wiring regulations.

Excessive leakage is when several of these small, individually harmless leaks add up. No single circuit is faulty, but the total is high enough that the RCD becomes oversensitive and trips on very little extra current.

A genuine earth fault is different again — a specific point where insulation has failed, a live conductor is touching something it shouldn’t, or water has created an unintended path to earth. This is what most people picture when they hear “earth fault,” and it’s the one that needs finding and repairing rather than managing.

Why Your RCD Trips When Nothing Seems Wrong?

Every circuit in your home contributes a small amount of standing leakage — current that leaks to earth constantly, as a normal by-product of the wiring and the appliances plugged into it. On its own, each contribution is tiny. Added together across ten or twelve circuits, it isn’t always tiny.

Domestic RCDs are supposed to trip at 30mA, but in practice many trip closer to 15–20mA because of ordinary manufacturing tolerances combined with that background leakage. If your circuits are already sitting at, say, 17mA of combined standing leakage, the RCD only needs a further 6–8mA to push it over the edge — and a fridge motor starting, a tumble dryer heating up, or a fluorescent fitting switching on can easily supply that.

A worked example. Imagine a consumer unit protecting eleven circuits on one RCD. A recently repaired kitchen ring contributes 6mA. A garage circuit with an older cable run contributes 3mA. The remaining nine circuits contribute small, ordinary amounts — half a milliamp here, a milliamp there. Add it up and the whole installation might be sitting at 15–17mA before anything switches on. Nothing on that list is faulty. But the RCD is now sensitised, and something like a tumble dryer starting can be enough to tip it into tripping.

This is a real, recognised pattern BS 7671 sets a guideline limit for standing leakage of no more than 30% of the RCD’s rated trip current, which works out to roughly 9mA on a standard 30mA device. Go meaningfully above that, and nuisance tripping becomes far more likely even though nothing on the installation is technically broken.

The practical fix isn’t to hunt for one faulty item, because there usually isn’t one. It’s to spread the circuits across more than one RCD typically by fitting RCBOs, which give each circuit its own individual protection instead of sharing one device between many. A circuit with its own RCBO can only be tripped by leakage on that circuit, not by the combined total of everything else in the house.

What Causes Earth Leakage?

Where genuine excessive leakage does have a specific source, it usually comes from one of the following.

Insulation breakdown. Cable insulation degrades with age, heat and mechanical stress. As it deteriorates, small amounts of current start finding a path to earth through the damaged section.

Moisture ingress. Water is an excellent conductor of the small currents involved. Damp junction boxes, outdoor sockets, garden lighting cables and bathroom fittings are common places for moisture to create a leakage path, particularly after rain.

Faulty appliances. Heating elements in kettles, washing machines, dishwashers and ovens are a frequent source. As the element or its wiring ages, leakage current increases, sometimes only becoming noticeable once the appliance heats up.

Capacitive leakage from electronics. Modern appliances and electronics — computers, LED drivers, some kitchen equipment — include filtering components that leak a small amount of current to earth by design. Individually harmless, but they add to the standing leakage total described above.

Physical damage. A cable nailed or screwed through during decorating, rodent damage in a loft, or a pinched cable behind a fitting can all create a direct leakage path.

Type AC vs Type A: Why Modern Homes Trip Older Boards

This is worth knowing if your consumer unit is older than your appliances.

Standard Type AC RCDs are designed to detect smooth, sine-wave leakage current. That covers most traditional loads without issue. But a lot of modern electronics LED drivers, induction hobs, EV chargers, solar inverters can produce a different kind of leakage current that a Type AC device doesn’t always detect reliably, or that can desensitise it over time.

Type A RCDs are designed to handle this modern leakage pattern properly. If a household has added an EV charger, solar panels or a lot of newer electronics onto a consumer unit that predates them, the protective devices may no longer match the loads they’re protecting. This is one of the more common reasons an older installation starts tripping more often after new equipment is added, and it’s something worth raising if you’re planning an EV charger install.

How Does an Electrician Measure Earth Leakage?

Diagnosing genuine earth leakage properly relies on more than reading the symptom.

Half-split isolation. The affected circuits are divided into groups, then progressively narrowed down by switching sections off and on, to identify which part of the installation is contributing the leakage.

Leakage clamp meter. A clamp meter placed around live and neutral together, without breaking the circuit, can measure the actual leakage current on a live circuit and show whether it’s within normal limits or genuinely excessive.

Insulation resistance testing. With the circuit safely isolated, an electrician tests the resistance between conductors and earth at 500V DC. A healthy circuit should read well above the minimum acceptable value; a reading close to or below it points to deteriorating insulation as the cause.

This combination is what separates “your RCD keeps tripping” from “your RCD keeps tripping because of X” the difference between a symptom and a diagnosis. It’s the same systematic approach covered in our guide to how electricians find electrical faults, applied specifically to a leakage problem rather than a wiring or connection fault.

What Can You Safely Check Yourself?

Before calling an electrician, there are a few safe observations that can genuinely help narrow things down:

• Which circuit or RCD is tripping, if that’s shown on the consumer unit
• Whether the trip happens at a particular time of day, or with a particular appliance running
• Whether it happens more often after rain, or when outdoor sockets are in use
• Whether unplugging everything on the affected circuit and reconnecting items one at a time stops the tripping

What you shouldn’t do is open the consumer unit enclosure, remove socket fronts, or attempt insulation resistance testing yourself. These measurements need the circuit properly isolated and proved dead first, and misreading them can be dangerous.

Arif, one of our electricians, recently worked through exactly this kind of investigation for a customer Tracy Pereira described how he quickly assessed a leakage situation on her property and got it resolved. That’s the shape most earth leakage jobs take: a specific check to confirm where the leakage is coming from, then a targeted fix, rather than guesswork.

Is Earth Leakage Dangerous?

It depends which category it falls into.

Normal, low-level leakage within regulation limits isn’t dangerous it’s an accepted part of how electrical systems work, and it’s exactly what your RCD is designed to tolerate.

Excessive leakage from accumulated small sources is usually more of an inconvenience than a safety risk, though it’s still worth investigating, since it can mask a genuine problem hiding among the smaller contributors.

A genuine earth fault is different. Damaged insulation or a live conductor finding an unintended path to earth is a real safety issue, which is precisely why the RCD is designed to disconnect the circuit immediately when it detects it. If your RCD trips and won’t reset, don’t keep resetting it repeatedly that’s a sign of a fault that needs identifying rather than working around.

What Does Earth Leakage Mean on an EICR?

If an EICR identifies leakage above an acceptable level, it’s usually coded as a C2 potentially dangerous, requiring urgent remedial work or, if the inspector can’t fully confirm the source on the day, as an FI, meaning further investigation is needed.

Either code makes the report Unsatisfactory. If you’ve had this flagged on a landlord EICR, our guide to electrical fault finding vs an EICR explains what happens next and the timeframe for getting it resolved.

When Is Splitting Circuits Onto RCBOs the Right Fix?

If testing shows the problem is cumulative standing leakage rather than one faulty item, replacing a single shared RCD with individual RCBOs on each circuit is usually the long-term solution. Each circuit then has its own dedicated protection, so leakage on one no longer affects the others, and a fault on one circuit doesn’t take down the rest of the house.

This is a consumer unit-level change, not a quick fix. Our guide to MCBs, RCDs and RCBOs explains how the three protective devices differ and where RCBOs fit into a modern board.

What Affects the Cost of Investigating Earth Leakage?

Cost depends mainly on how much diagnostic work is needed before the cause is confirmed. A leakage source that’s isolated quickly with a clamp meter reading is a shorter job than one that needs half-split isolation across several circuits, or insulation resistance testing on multiple sections.

If the outcome is a straightforward repair a damaged section of cable, a faulty appliance connection that’s separate from the diagnostic time. If the fix is splitting circuits onto RCBOs, that’s consumer unit work and is quoted separately again. As with any fault-finding job, the electrician needs to understand what’s involved before giving an accurate price.

Frequently Asked Questions

Is earth leakage the same as an earth fault? 

Not always. Earth leakage can mean a genuine fault, but it can also mean several small, normal leaks adding up to a level that trips the RCD. The two need different responses — one needs repairing, the other needs managing.

Why does my RCD trip only sometimes? 

This is often standing leakage close to the trip threshold, tipped over occasionally by an appliance drawing extra current when it starts up, such as a fridge motor or a tumble dryer heating element.

Can a faulty appliance cause earth leakage? 

Yes. Ageing heating elements, damaged appliance cables and degraded internal insulation are common sources, and they often only leak noticeably once the appliance is running or has warmed up.

Does rain cause earth leakage? 

Yes, frequently. Moisture creates a conductive path between live conductors and earth, particularly in outdoor sockets, garden lighting and any joint that isn’t fully weatherproofed.

Will an electrician need to replace my consumer unit? 

Not necessarily. Many earth leakage issues are resolved by repairing a specific fault. RCBOs and a new consumer unit are only needed if the diagnosis shows the RCD is overloaded with cumulative leakage from many circuits.

Is it safe to keep resetting a tripping RCD? 

No. If it trips again immediately, that suggests an active fault rather than a passing nuisance trip, and repeatedly resetting it doesn’t resolve the underlying cause.

What’s the difference between a Type AC and Type A RCD? 

Type AC RCDs detect standard sine-wave leakage current. Type A RCDs are designed to also detect the leakage patterns produced by EV chargers, solar inverters and some modern electronics, which older Type AC devices can miss or become desensitised by.

How is earth leakage tested? 

An electrician can measure live leakage current with a clamp meter without breaking the circuit, and test insulation resistance with the circuit safely isolated to confirm whether cable insulation has deteriorated.

Need Earth Leakage Diagnosed in Hounslow or West London?

If your RCD keeps tripping and you’re not sure whether it’s a nuisance trip or a genuine fault, Handy Electric Pro provides electrical fault finding across Hounslow, Twickenham, Feltham, Isleworth, Richmond, Brentford and the wider West and South West London area.

Muhammad Arif is an ECS Gold Card qualified electrician and NAPIT-approved contractor. All diagnostic work is carried out to BS 7671:2018, and where a repair or consumer unit change is needed, the appropriate certificate is issued on completion.

If your RCD keeps tripping and resetting it isn’t solving anything, contact us for a same-day or next-day investigation.

Call or WhatsApp: +44 7389 775236 Available 24/7 for urgent electrical faults.